1. Field of the Invention
The subject invention relates to a manifold apparatus for a plurality of liquid filtration segments wherein filtration is effected by tangential flow of the liquid across a filter surface, and more particularly, to a distributor plate for crossflow cassette-type filtration appliances which permits stacking of a plurality of filtration modules wherein liquid is introduced and removed from the filtration module under conditions to provide improved separation of filtrate species from retentate species.
2. Description of the Related Art
Crossflow cassette filtration apparatus usually consist, according to the state of the art, of a holder, filter cassettes and end plates. The holder receives the end plates and at least one filter cassette, which is sealingly pressed between the end plates. For that purpose the end plates are arranged on the holder to be movable on one another. At least one end plate is constructed as a distributor plate with connections for the feed of liquid, which is to be filtered, into the filter cassettes and for the discharge of concentrate and filtrate from the filter cassettes. If the feed and/or discharge of the fluids takes place merely at one surface of the distributor plate, the plate is termed a monodirectional distributor plate and if the feed and/or discharge of the fluids takes place at the front and back surface of the distributor plate, it is termed a bi-directional distributor plate. In the latter case, the filter cassettes are arranged at both ends at the front and back surface of the distributor plate.
In DE-OS 34 41 249, there is described a crossflow cassette filtration device in which the filter cassettes are clamped between two end plates respectively constructed as distributor plates. It is disadvantageous that the connections at the two distributor plates cannot be fixedly piped in, because the distributor plates have to be moved on one another for the clamping of the filter cassettes in place. Fixed piping would, however, significantly increase the filtration reliability, inclusive of the capability of the device to be sterilized, which is particularly important in sensitive areas of filtration, for example, the pharmaceutical or biotechnological field.
U.S. Pat. No. 4,715,955 describes a crossflow cassette filtration apparatus consisting of holder, filter cassette and end plates, wherein one of the end plates is constructed as a monodirectional distributor plate at which are arranged all the connections for the feed and discharge of the fluids. A design of this distributor plate as a bi-directional distributor plate is discussed in EP 0 345 209 B1, or its equivalent U.S. Pat. No. 4,849,102. In both cases, the distributor plates have opposite planar front and back surfaces, opposite narrow first and second side walls, opposite narrow first and second edge walls, a respective connection for the feed of liquid to be filtered and for the discharge of concentrate and two connections for the discharge of filtrate. The front surface or the front and back surfaces have mutually spaced openings which agree with corresponding openings of the filter cassettes to be connected to the distributor plate. The openings for the feed of liquid to be filtered and a first number of openings for the discharge of filtrate lie on a straight line parallel to the first narrow edge wall, and the openings for the discharge of concentrate and a second number of openings for the discharge of filtrate lie on a straight line parallel to the second narrow edge wall. The first number of openings for the discharge of filtrate open at an acute angle with respect to the front surface or the front and back surfaces into a first channel, which extends parallel to the first narrow edge wall and to the front and back surfaces. It exits from the distributor plate at at least one of the side walls. The second number of openings for the discharge of filtrate open at an acute angle with respect to the front surface or front and back surfaces into a second channel, which extends parallel to the second narrow edge wall and to the front and back surfaces. It exits from the distributor plate at at least one of the side walls.
It is disadvantageous that the connection for the feed of liquid to be filtered and the connection for the discharge of concentrate are effected at, respectively, the end of the first channel and the end of the second channel from one of the side walls. This configuration leads to an undesired pressure decay in the direction of the end, which is opposite to the connection, of the channels, which continues on over the membrane surfaces. This pressure gradient leads to a non-uniform flowing over and through the membrane surfaces and thus to a non-uniform utilization of the membrane surfaces of the filter cassette, which has as a consequence a reduction in the filtration performance and a premature blocking of the membranes in the more strongly loaded regions.
Thus, there is a need for a distributor plate for cassette filtration apparatus which may enable an improved filtration performance and a longer service life of the cassette filtration apparatus.
Additionally, the distributor plates of the prior art are made of a unitary construction with standard pipeline connections. However, throughout the world, there are different pipeline standards which all differ in terms of diameter and wall thickness. By the way of an example, a pipeline of nominal width DN25 may have the following internal diameter: ISO standard xe2x88x9230.5 mm; DIN standard 11851 xe2x88x9225 mm; SMS standard xe2x88x9222.5 mm; and BSOD standard (inches) xe2x88x9222.1 mm. Since the holders of filtration apparatus are usually integrated into existing surroundings, the pipeline standard which is customarily employed by a user must be used. Furthermore, for the design of an overall installation to comply with good manufacturing practices, it is absolutely imperative to ensure a transition which is in no way mismatched.
Typical filtration apparatus employ connections which only correspond to one standard and have to be reduced accordingly in any given installation. Adapting of the holders and/or distribution plates is only possible with a considerable structural outlay because of the offset bores of varying manufacturers since it is usually necessary to change the angle of the bores.
Therefore, there is a further need for a distributor plate for cassette filtration apparatus which are easily adaptable for varying pipeline standards and varying installation configurations.
In accordance with the present invention, a distributor plate assembly for crossflow cassette-type filtration appliances is provided which consists of three parts and is used in the ultrafiltration or microfiltration of liquids. The three-part distributor plate assembly comprises a middle plate member, an upper plate member and a lower plate member, which when combined in use has a front surface and rear surface, a first and second side wall and a first and second edge wall.
The middle plate member receives a feed duct and a residue duct which run parallel to the edge walls and to the front surface and rear surface and emerge at least from one of the side walls. The feed duct is connected via feed connecting ducts to feed orifices on the front surface and/or rear surface of the middle plate. The feed orifices are arranged congruently to corresponding feed orifices of a filtration module. The residue duct is connected via residue connecting ducts to residue orifices on the front surface and/or rear surface of the middle plate. The residue orifices are arranged congruently to corresponding residue orifices of a filtration module.
Furthermore, the middle plate member includes on its front and/or rear surface upper and lower filtrate orifices which are arranged congruently to corresponding filtrate orifices of the filtration module. The upper filtrate orifices are connected in a communicating manner to an upper filtrate collecting chamber via upper filtrate connecting ducts. In the first embodiment of the three-part distributor plate, the filtrate collecting chamber is designed as a depression in the first edge wall of the middle plate member. In the second embodiment, the filtrate collecting chamber is designed as a depression in the edge wall of the upper plate member, which faces the first side wall of the middle plate member. The lower filtrate orifices are connected in a communicating manner to a lower filtrate collecting chamber via lower filtrate connecting ducts similar to the manner for the upper filtrate orifices.
The different embodiments of the three-part distributor plate assembly of the subject invention varies by the configuration of the upper and lower plate members, which allows the distributor plate assembly to be adapted to different installations without redesigning the distributor plate. In the first embodiment, the upper plate member receives a filtrate duct which runs parallel to the edge walls and to the front and rear surface and emerges at least from one of the side walls. The filtrate duct is connected in a communicating manner to the upper filtrate collecting chamber of the middle plate member via one or more longitudinal filtrate duct orifices. Similar to the upper plate member, the lower plate member receives a filtrate duct which runs parallel to the edge walls and to the front and rear surfaces and emerges from at least one of the side walls. The filtrate duct is connected in a communicating manner to the lower filtrate collecting chamber of the middle plate member via one or more longitudinal filtrate duct orifices.
In the second embodiment, the upper plate member receives a short filtrate duct which runs perpendicular to the edge walls and at right angles to the front and rear surface and emerges from the edge wall of the upper plate member. The filtrate duct is connected in a communicating manner directly to the upper filtrate collecting chamber of the upper plate member. Similar to the upper plate member, the lower plate member receives a filtrate duct which runs perpendicular to the edge walls and at right angles to the front and rear surfaces and emerges from the edge wall of the lower plate member. The filtrate duct is connected in a communicating manner directly to the lower filtrate collecting chamber of the lower plate member.
Finally, in either embodiment, the upper and lower plate members are connected to the middle plate member via connections, for example screws, familiar to a person skilled in the art. Additionally, a fluidtight seal is implemented in the peripheral edge region of the filtrate collecting chambers, for example, by means of an O-ring seal.
Due to the manner of flow to and/or from associated filter cassettes or modules by way of a distributor plate assembly embodying the invention, it may be possible to achieve approximately the same pressure at all channels, which communicate with the said openings, of the filter cassettes. Thus, an equal flowing over the membrane surfaces in terms of area and an equal flowing through the membranes in the filter cassettes may be ensured, which may produce an increase in the filtration performance by up to 15% and an approximately equivalent extension of the service life of a cassette filtration apparatus equipped with such a distributor plate assembly.
Furthermore, the three-part construction allows the distributor plate assembly to be adapted for various installations. By having the ability to change the diameter of the ducts in the end plate member, the other bores of the plate remain unchanged and the distributor plate assembly does not have to be redesigned. Additionally, the distributor plate member can be custom made to the user""s existing installation without external adaptors resulting in reduced dead space and a more compact overall design.
These and other features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.